Caratterizzazione di β-lattamasi a spettro esteso (ESβL) prodotte da isolati clinici di Pseudomonas Aeruginosa ceftazidime-resistenti

Pseudomonas aeruginosa shows intrinsic resistance to a wide variety of antimicrobial agents, including most β-lactams. This is a major problem in hospitals because P aeruginosa is a frequently encountered opportunistic pathogen and a leading cause of nosocomial infections. In this species, the overproduction of chromosomal-encoded cephalosporinase is the most clinically relevant mechanism of resistance limiting the potency of β-lactam molecules. Over the last few years various extended-spectrum β-lactamases (ESβLs) have been found in P aeruginosa, most of them conferring high-level resistance to expanded-spectrum anti-Pseudomonas cephalosporins such as ceftazidime. Recently the prevalence of strains with acquired resistance to ceftazidime has risen significantly in Italy. The aim of the present study was i) to investigate the prevalence of extended spectrum β-lactamases production in ceftazidime resistant P. aeruginosa isolates collected from three different hospitals in Northern Italy and ii) to delineate the relationships among ESβL-producing strains. The synergy with clavulanate was studied in 99 cefazidime-resistant clinical isolates, 31 of these (31%) resulted to be positive. The analysis through isoelectric focusing of crude enzymatic extracts obtained from these strains and the overlaying procedure revealed the production of ESβLs able to hydrolize ceftazidime at different isoelectric points. Molecular analysis identified the production of PER-1 enzyme in 21 of the ESβL-producer strains (64%). The genotype analysis, carried out by Pulsed-Field Gel Electrophoresis, revealed different pulsotypes. The variety of clones and the prevalence of PER-1 producers show high diffusion potential of the blaPER-1 determinant.